1. Field of the Invention
This invention relates to a valve driving apparatus for actuating a shutoff valve or a dump valve provided in a pipeline for conveying a gaseous or liquid substance.
2. Description of the Related Art
In a gas pipeline, for example, shutoff valves are installed at various positions on the route along which the pipeline is laid. It is known in the art to operate such a shutoff valve by means of an actuator which uses, as the power source force thereof, the gas pressure in the pipeline to be extracted therefrom in the vicinity of the seat of the shutoff valve. In this case, however, the apparatus is dangerous because the spent gas emanating from the actuator is released into the open air. Where the gas so released into the open air has the possibility of doing harm to men and beasts, the gas pressure of the pipeline cannot be utilized as the power source. Thus, it is necessary to resort to the practice of additionally providing a separate pressure cylinder of air, nitrogen, or carbon dioxide and utilizing this cylinder as a power source for the actuator.
When the pressure cylinder is used as mentioned above, the pressure of the cylinder actuates the shutoff valve by overcoming the gas pressure of the gas pipeline and, therefore, must be higher than the pressure required by the actuator. Since the cylinder has a limited capacity, the shutoff valve in the process of switching may possibly cease to operate due to a shortage of pressure. The cylinder, therefore, demands enormous labor for replenishment of its content or replacement of the cylinder itself for a new supply. Further, if the replenishment or replacement of the cylinder mentioned above is incomplete, the pressure cylinder will possibly fail to actuate the shutoff valve and consequently cause an accident or even endanger the operation of the gas pipeline.
An object of this invention is to provide a valve driving apparatus which safely uses the gas pressure of a gas pipeline as the power source for the actuator which serves to operate a shutoff valve or a dump valve in the pipeline without causing the spent gas pressure to leak into the ambient air and harm and, moreover, completely obviates the necessity for relying on a pressure cylinder of air, nitrogen, or carbon dioxide as the power source.
In the case of a driving apparatus which uses the gas of a pipeline as the power source for an actuator as mentioned above, and incorporates therein a closed gas line so constructed as to return the gas to the pipeline, if the pressure of the pipeline is lowered, the shutoff valve will possibly fail to operate normally.
It is conceivable herein to provide a gas tank filled with a compressed nonflammable gas and a booster which are separately disposed. If the gas tank and the booster are so constructed as to be connected to each other with a pipe, the apparatus will have the possibility of producing a defective operation on account of the leak through the point of connection. Further, since the booster and the gas tank are separate entities, the space for their installation is so large as to render it difficult to make the driving apparatus compact.
Another object of this invention is to provide a valve driving apparatus which promotes a reduction in size of the apparatus by disposing a booster within a gas tank, and enables the gas pressure in the gas tank to remain constantly at a prescribed level by causing the fluid flowing through the pipeline to fill the gas tank automatically when the gas pressure in the gas tank falls below the prescribed level during operation of the booster. Thus, the present invention obviates completely the necessity for replenishing the gas tank or replacing the cylinder, suffers only few leaky points, and excels in safety and economy.